In a power conversion system such as a variable speed, constant frequency (VSCF) power generating system, a generator converts variable speed motive power supplied by a prime mover into variable frequency AC power. The variable frequency power is rectified and provided over a DC link to a controllable inverter. The inverter, which comprises one or more subinverters and a summing transformer, is operated to produce constant frequency AC power, which is then supplied, over a load bus, to loads requiring such power. In various applications, such as an aircraft jet engine, the size and weight of the summing transformer used in such a system is extremely important.
The physical structure of a summing transformer for use in a VSCF system such as that described above must accommodate the specific electronic system that is intended to be used. One such electronic system is a star-delta system. An example of a star-delta system that may be used in an inverter in a VSCF system may be found in Dhyanchand, et al., U.S. patent . applications Ser. Nos. 07/421,830, filed Oct. 16, 1989, entitled "Power Conversion System With Stepped Waveform DC/AC Converter Having Prime Mover Start Capability" and 07/426,444, filed Oct. 25, 1989, entitled "Power Conversion System with Stepped Waveform DC to AC Converter Having Prime Mover Start Capability". The star-delta systems of these applications include a 24-step inverter comprised of four subinverters and a summing transformer, and produce a 24-step, three-phase output. Each of the four subinverters is coupled to an associated set of three primary windings, which are carried on the summing transformer. Two of these associated sets of primary windings are connected in wye (or "star") configuration. The other two sets of primary windings are connected in delta configuration. The three-phase output is developed through magnetic linkage of three selected groups of primary windings with secondary windings also carried on the transformer. Each of the selected groups of primary windings comprises one primary winding from each of the four sets of primary windings. While in some electronic systems, such as that disclosed in Compoly, et al., U.S. Pat. No. 3,775,662, each group of primary windings is magnetically linked with four secondary windings, in the system disclosed in the Dhyanchand applications each such group is magnetically linked with a single secondary winding.
One problem faced by those skilled in the art has been to construct a transformer capable of accommodating the electronic system described in the Dhyanchand applications while meeting weight and size limitations critical in typical applications, such as in an aircraft jet engine.